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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <CAJfpegshWgUYZLc5v-Vwf6g3ZGmfnHsT_t9JLwxFoV8wPrvBnA@mail.gmail.com>
References: <CAJfpegshWgUYZLc5v-Vwf6g3ZGmfnHsT_t9JLwxFoV8wPrvBnA@mail.gmail.com> <20230214171330.2722188-1-dhowells@redhat.com> <20230214171330.2722188-6-dhowells@redhat.com>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     dhowells@redhat.com, Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>,
        linux-unionfs@vger.kernel.org
Subject: [PATCH v15 05/17] overlayfs: Implement splice-read
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Date:   Wed, 15 Feb 2023 15:40:58 +0000
Message-ID: <3370085.1676475658@warthog.procyon.org.uk>
Precedence: bulk

How about the attached then?

David
---
overlayfs: Implement splice-read

Implement splice-read for overlayfs by passing the request down a layer
rather than going through generic_file_splice_read() which is going to be
changed to assume that ->read_folio() is present on buffered files.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: John Hubbard <jhubbard@nvidia.com>
cc: David Hildenbrand <david@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Miklos Szeredi <miklos@szeredi.hu>
cc: linux-unionfs@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
Notes:
    ver #15)
     - Remove redundant FMODE_CAN_ODIRECT check on real file.
     - Do rw_verify_area() on the real file, not the overlay file.
     - Fix a file leak.

 fs/overlayfs/file.c |   33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index c9d0c362c7ef..72a545da51a2 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -419,6 +419,37 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, str=
uct iov_iter *iter)
 	return ret;
 }
 =

+static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
+			       struct pipe_inode_info *pipe, size_t len,
+			       unsigned int flags)
+{
+	const struct cred *old_cred;
+	struct fd real;
+	ssize_t ret;
+
+	ret =3D ovl_real_fdget(in, &real);
+	if (ret)
+		return ret;
+
+	ret =3D -EINVAL;
+	if (!real.file->f_op->splice_read)
+		goto out_fdput;
+
+	ret =3D rw_verify_area(READ, real.file, ppos, len);
+	if (unlikely(ret < 0))
+		goto out_fdput;
+
+	old_cred =3D ovl_override_creds(file_inode(in)->i_sb);
+	ret =3D real.file->f_op->splice_read(real.file, ppos, pipe, len, flags);
+
+	revert_creds(old_cred);
+	ovl_file_accessed(in);
+out_fdput:
+	fdput(real);
+
+	return ret;
+}
+
 /*
  * Calling iter_file_splice_write() directly from overlay's f_op may dead=
lock
  * due to lock order inversion between pipe->mutex in iter_file_splice_wr=
ite()
@@ -695,7 +726,7 @@ const struct file_operations ovl_file_operations =3D {
 	.fallocate	=3D ovl_fallocate,
 	.fadvise	=3D ovl_fadvise,
 	.flush		=3D ovl_flush,
-	.splice_read    =3D generic_file_splice_read,
+	.splice_read    =3D ovl_splice_read,
 	.splice_write   =3D ovl_splice_write,
 =

 	.copy_file_range	=3D ovl_copy_file_range,